Aim: to analyze the learning curve of surgeons while performing laparoscopic partial nephrectomy in patients with localized renal parenchymal lesions by calculating the MIC (negative surgical margin, ischemia, and complications) index depending on tumor complexity according to the R.E.N.A.L. and PADUA nephrometric scores.
Materials and methods: the retrospective study included the results of laparoscopic partial nephrectomies in 320 patients with localized renal parenchymal lesions. The procedures were carried out by four surgeons from the Institute of Urology and Human Reproductive Health of FGAOU VO I.M. Sechenov First Moscow State Medical University, Moscow, Russia (EC-1; ESH-4; EB-7; ME-13) from January 2014 to June 2019. At baseline, all operators had experience of performing at least 30 laparoscopic interventions. In addition to the standard preoperative examination, a 3D virtual planning was carried out using the Amira 3D modeling program. In all cases, the nephrometric assessment of complexity was performed according to the R.E.N.A.L. and PADUA scores. The learning curve was assessed based on the results of operations based on the MIC index. All surgical interventions were divided into eras. In the era, 40 consecutive procedures for each operator were evaluated. Acquired skills were assessed over two eras.
Results. The average age of patients, of which 191 (59.7%) were men, was 54.4±11.37 years. The average body mass index was 28.55±3.85 kg/m2, the absolute volume of kidney lesions was 26.72±43.72 cm3, the average Charlson comorbidity index was 1.46±1.29, the average R.E.N.A.L. and PADUA scores were 6.38±1.75 and 7.92±1.51, respectively, the average duration of procedure was 150.36±50.18 min, the average blood loss was 227.94±280.22 ml, the average time thermal ischemia was 13.28±7.82 min. Postoperative complications were seen in 36 (11.2%) cases, of which grade III and more according to Clavien-Dindo developed in 8 patients (2.5%). A positive surgical margin was found in 4 (1.2%) patients. The overall MIC index was achieved in 243 (75.9%) cases; in era 1 it was seen in 71.9% cases in comparison with 80% in era 2. With the 1st degree of complexity (152 (47.5%) patients), MIC was achieved in 80.9% of cases, compared to 76.6% and 56.8% in patients with 2nd degree of complexity (n=124, 38.8%) and 3rd degree of complexity (n=44, 13.8%), respectively. Rate of MIC achievement in eras 1 and 2 for different surgeons were as following: 65% and 72.5%, 75 and 80%, 87.5 and 85% and 60 and 82.5%, for operator 1, 4, 7 and 13, respectively. Age, tumor complexity, R.E.N.A.L. score and PADUA score were the most significant parameters for determining MIC, identified on the basis of the criterion of equality of group means of discrete analysis.
Conclusion. In all surgeons, the MIC index increased with the accumulation of experience in performing laparoscopic partial nephrectomy, but was lower with an increased degree of complexity of procedures. The minimum number of laparoscopic partial nephrectomies required to achieve an MIC ≥ 70% should be at least 40.

Keywords: renal cell cancer, partial nephrectomy, laparoscopy, 3D modeling, learning curve, nephrometry, MIC